Control system for regulating the rate of flow of liquids or other materials capable of flowing



Oct. 3, 1950 w. K. PORTEOUS CONTROL SYSTEM FOR REGULATING THE RATE OF FLOW OF LIQUIDS OR OTHER MATERIALS CAPABLE OF FLOWING Filed July 24, 1944 4 Sheets-Sheet 1 A Horney Oct. 3, 1950 w. K. PORTEOUS 2,524,540

CONTROL SYSTEM FOR REGULATING THE RATE OF FLOW OF LIQUIDS OR OTHER MATERIALS CAPABLE 0F FLQWING Filed July 24, 1944 4 Sheets-Sheet 2 FIG 3.

QLL/ 6 Inventor Maw A. [Mow A llorney Oct. 3, 1950 w. K. PORTEOUS 2,524,540

CONTROL SYSTEM FOR REGULATING THE RATE OF FLOW OF LIQUIDS OR OTHER MATERIALS CAPABLE OF FLOWING Filed July 24, 1944 4 Sheets-Sheet 3 I n venlor Attorney 01d. 3, 1950 w K PORTEOUS 2,524,540

CONTROL SYSTEM FOR'RECULATING THE RATE OF FLOW 0F LIQUIDS OR OTHER MATERIALS CAPABLE OF FLOWING Patented Oct. 3,, 1950 CONTROL SYSTEM FOR REGULATING THE RATE OF FLOW OF LIQUIDS OR OTHER MATERIALS CAPABLE OF FLOWING William King Porteous, St. Margarets, England, assignor of fifteen one-hundredths to Towler & Son Limited, London, England Application July 24, 1944, Serial No. 546,368 In Great Britain August 12, 1943 8 Claims.

This invention relates to control systems for regulating the rate of flow of liquids or other materials capable of flowing. The invention is particularly applicable to systems in which a liquid or other material capable of flowing is pumped through a treatment apparatus, and in which the rate of flow is controlled by an automatic valve in the circuit and conveniently in the discharge outlet from the apparatus.

In order to set forth some definite practical applications of the invention, it may be explained that liquid or other material capable of flowing, frequently has to be treated in a number of tanks which have to be filled with the material and have to be discharged in sequence at recurring intervals. It is necessary to arrange that while one vessel is being filled, another is being emptied, and also during that time the contents of one or more further tanks have to undergo some form of treatment so that each tank and its contents is taken in turn through the same cycle of operations. One example of a liquid which may have to be dealt with in that way is concerned with the pasteurisation of milk; one tank may be filled with milk at a predetermined rate so that the filling may take some time, while simultaneously a second tank in which the milk has been pasteurised is being emptied, and the milk in a third tank or in morethan one additional tanks is quiescent and undergoing the pasteurising treatment at the same time. Similar cyclic treatments are necessary sometimes in the case of powdered, granular, or quasi-liquid materials, an example of the last mentioned being the treatment of sewage sludge which has to undergo a heating or cooking treatment for a given period. An example of such an apparatus for treating sewage sludge is particularly described in application Serial No. 456,073, filed August 2 5, 1942, now Patent 2,372,448. The problem in each of these cases is so to co-ordinate the operations in the difierent tanks that among other things, the emptying of one tank is completed practically simultaneously with the filling of another tank.

The invention is particularly suitable for use in connection with the discharge pipe from such a cyclic treatment apparatus but is not limited to such apparatus.

According to the invention, an automaticallyoperated valve is interposed in the path of flow of the liquid or other material, and the resistance in the valve naturally causes a fall in pressure, and the arrangement is such that the reduced pressure on the outlet side from the valve is balanced, for example, in a cylinder against a constant force which may be provided by a counterweighted lever or by a spring and so forth. The result of this arrangement is that if the flow through the valve is seriously impeded at any time, for example, by partial blocking of the valve passage by solid or other foreign matter, the increase in resistance in the valve produces an increase in the pressure drop with a consequent reduction in the pressure on the outlet side so that the piston in the cylinder is moved by the counterweight or other constant force, and by linking the moving piston to the valve, the latter is then opened considerably to clear the obstruction, whereupon the pressure on the outlet side again rises, causing the return of the piston and the moving parts so that the valve opening is again restored to normal and normal conditions of flow again take place. In the preferred form,

a pivoted lever is linked to the piston of the example, to a fairly large scale apparatus for the treatment of sewage sludge, a further automatic control may be combined with a valve of the kind referred to above. In that case, following the valve already referred to is another similar valve in the discharge pipe from the apparatus with a length of pipe between the two valves sufficient to provide a volume of the material under treatment which will operate the valves. The second valve, while being similar in construction to the first, produces a second drop in pressure and is controlled by a similar piston and cylinder, the latter being connected to the pressure after the first valve and before the sec-' ond valve, that is, what may be called the intermediate pressure, and the piston being acted upon by a counterweight which in this case is mounted so as to be capable of movement along the pivoted lever in either direction under the influence of a screw driven by an electric motor.

In this case, the electrical control is similar' to that set forth in the specification of application Serial No. 456,073 referred to above, the

screw for adjusting the counterweight being driven through an impulse motor in such a way that if one tank is emptied before another tank i which is being filledat the same time is com- I 3 pletely filled, the impulse motor receives an impulse of such a sign that the counterweight is moved a predetermined distance away from the pivot of its lever. The result is that the opposing pressure has to beincreased automatically, which results in slight closing of the valve and slight reduction in the rate of discharge. If the reverse takes place and one tank is emptied rather.

too slowly, the impulse motor receives an impulse of opposite sign so as to move the counterweight the same distance towards its pivot, with the result that the automatic valve is slightly opened and the rate of discharge increased.

As an additional safeguard, it is possible to arrange a solenoid associated with the second valve to close that valve if, in the tank which is being emptied at any time, the sludge reaches.

In; order that the invention may be clearly understood and readily carried into effect, an example of its application to the control of the discharge from a sludge treating plant of the kind already-referred to, will now be more fully describedby way of example with reference to the accompanying drawings, in which:

Figure; 1 is aside elevation, and

Figure 2 a plan of the arrangement of'valves anditheir operating members in the discharge pipefroin the sludgetreating plant;

Figure 3' is a longitudinal vertical section of ther-frrst valve; and

Figure 4 is a section at right-angles to Figure 3 taken on the line IV-IVin Figure 3;

Figure 5 is a frontelevation of the second valve and the associated parts; while Figure 6 is an explanatory circuit diagram.

Referring to Figures 1 and 2', I isthe discharge manifold for the treated sludge from a plant;

for example, as set forth in the specification of application Serial No. 456,073 referred to above. The-flow through this pipe can be controlled-by a pair of ordinary screw-down stop valves shown at 2 and 2a. Following the stop valve 2 is the automatically-operated valve 3 whichis shown in greater detail in Figures 3 and 4. The valve is a slide valve consisting of a vertically sliding gate 4 which is a hardened plate with a through-passage 5 co-operating with an insert 6 forming-a fiat seating. It will be appreciated that this valve imposes a resistance on the flow of the sludge which takes place in the direction of the arrows I so that a fall of pressure occurs in the valve with a reduction of pressure on the outlet side, which is the right-hand side in Figures 1 and .3.

This reduced pressure on the outlet side is communicated by means of a pipe 8 to the lower end of a control cylinder 9. This reduced pressure, therefore, operates on the-under surface of a. piston in the cylinder 9, the piston however, notrbeing shown. This pressure under normal operation is counterbalanced by a constant force provided-rin the form illustrated by a lever l0 bearing; a counterweight H. Thus valve 3 is normally biased towards open position by counterweight H. The lever I0 is pivoted at l2 to the casing of the valve 3, and is furnished with a pair of centering springs [0a anchored at their outer ends to fixed brackets lb. The lever I0 is linked at l3 to the piston in the cylinder 9. It is also connected to the moving member 4 of the valve through an adjustable connection which is arranged as follows. A stem l4, which can be turned by a handwheel 15, passes through a bearing block 3 pivoted to the short arm of the lever l0 and is prevented from sliding in the bearing block by the handwheel l5 itself and a pinned-on collar II. The stem I4, however, is screw-threaded and screwed into a nut l8 carried in a short lever l9 which can turn on the pivot l2 of the lever [0. In driving connection with the lever [B is an arm 20 pivoted to a link 2| in its turn pivoted to the valve member 4. Hence, by rotating the handwheel i5, the lever l9 can beslightly rocked and the valve member 4 adjusted while-the lever I0 is stationary.

The result of this arrangement is that if the flow through the valve 3 is seriously impeded at any time, for instance by partial blocking of the aperture 5 in the valve member 4, or of the passage 22 through the seating 6 by solid or other foreign matter, the resistance in the valve increases with an increase in the pressure drop in the valve, and a consequent reductionin the pressure on the outlet side'so that the counterweight moves thepiston in the cylinder 9 down, andtherocking of the lever [0 through the stem l4, lever l9, arm 20, and link2l, raises the valve member cs0 that the valvepassage is opened considerably to clear the obstruction. As a consequence of-this, the pressure drop in the valve is reduced, the pressure on; the-outlet side again rises,causingthe-return upwardly of the piston,

in the cylinder 9, so that the moving parts are restored, the valve member 4- is moved down to the normal position; and-normal conditions of flow again takeplace.

The further automatic control which is associated with the valve mechanism described above comprises another similarvalve 23 shown in greater detail in Figure 5. It follows the valve 3 in the discharge manifold I; leaving a length of pipe la between'the valves-3 and 23 sufficient to provide a-volume of the treated'sludge which will operate the valves. The valve 23 while generally similarin construction to the valve 3, produces a second drop'in pressure inthe manifold 2, and is controlled by asimilar piston and cylinder 24, the latter beingin communication with the pressure in the pipe section la, following the valve 3 and preceding the valve 23. That is what may be called-the intermediate pressure,

The piston in the cylinder 24 is connected by a link 25 to a lever fi'generally similar to the lever l9 andcarrying a sliding counterweight 27. Connection between the'lever' 26 and the valve member-23 is exactlysimilar to theconneotion of the lever I!) with the valve 3-and is provided with means for adjustment comprising a handwheel 28-as before having a pivotal bearing in the short arm-of thelever 26* and screw-threaded into a nut 29 carried in a short lever 30 linked to the movable valve member 3| as before. In this case;- however, the lever 26 is,reversed as com pared with the lever-l0 so that the biasing force exerted by the; counterweight 2'! tends to close the. valve 23.-

In order that the counterweight 21 may be automaticallyv moved towards or, away from the fulcrum point 32 of the lever 26, the weight 2'! is horizontally bored and tapped and a lead-screw 33 is threaded into it. This lead-screw is driven by an intermittently operated electric motor 34. The operation of this motor will be referred to in greater detail in connection with Figure 6 of the drawings. It should be observed, however, that the lead-screw 33 has to rock with the lever 26 about the axis of the fulcrum 32 of that lever, and consequently is connected with the shaft 35 of the motor 34 through a coupling 36 which permits upward and downward movement of the lead-screw 33 about the axis of the fulcrum 32. The lever is shown with a pair of centralising springs 26a arranged in a similar fashion to the springs Illa.

The method of operation of the valve 23 under control of the motor 34 can be best explained with reference to Figure 6. This is a circuit diagram of the electric control system similar in general principles to that shown in the specification of application Serial No. 456,073 referred to above but modified in certain respects. Figure 6 will be appreciated from a consideration of the specification of application Serial No. 456,073 referred to above by the aid of the following remarks. As in the prior case, the relays RtL-Rel and Rfl are energised from a transformer Tr, when the respective tanks T, E and F are filled and the plungers 152, eg and f2 are raised. Similarly, relays RtZ, Re2, R Z are energised when the respective plungers t4, c4 and f4 are raised. The impulse motor 34 also shown in Figure 6 corresponds to the motor IM in the prior specification, and as in that case, is arranged so that it rotates a fixed amount in one direction when receiving a positive impulse, and the same amount in the opposite direction when it receives a negative impulse.

In order to explain the action, it is best to assume a particular state of afifairs, for example, in which the tank F is being filled, the tank E is being emptied, and the tank T is maintained filled and under treatment, as will be followed from the drawing of the specification of application Serial No. 455,073 referred to above. The tank F becomes filled in due course and the plunger f2 raised, and as indicated above, the relay Rfi is then energised. A current can then fiow from the transformer Trl, as seen in Figure 6, through contacts 3?, 38 of the relay R and contact segment 1 and arm I) of the distributor switch RS as in the said prior specification, to the motor starter MS in that specification, .so that the shaft 39 which corresponds to the shaft 3 in the prior specification is rotated clockwise through 120, whereupon the circuit is interrupted between the arm I) and segment f referred to above. The result of this is that the-inlet valve Fi is closed in order that the heat treatment of the sludge may go on in the tank F While the discharge valve Td is opened, so that emptying of tank T commences, and finally the discharge valve Ed is closed, and the inlet valve E2 is opened, so that filling of the tank E commences. All this can be followed from the prior specification of application Serial No. 456,073 referred to above. Y

If the tank F is filled before the tank E is completely emptied, the relay RJI will be energised, while the relay R62 still remains energised. The result of this is that there is a circuit from the transformer Trl through contacts ifi, i! of tiv relay RJI, through contacts 42, 43 of relay R62,

through the segment fo'of the distributor switch leaks in its valves.

DO, and then through the arm 0 of that switch,

through the conductor 5|, the motor reversing switch MRS and back through the conductors 4 1, 45 to the transformer Trl. The result of this is that the motor 34 receives an impulse in one direction. In these circumstances, it is desired to increase the rate of discharge and to increase the rate of emptying of each tank so that one tank may be emptied at the same time that the other is filled. Thisis effected by slightly opening the valve 23 so that th impulse which the motor 34 has received causes that motor and the lead-screw 33 to be rotated in such a direction as to cause the counterweight 21 to be moved a predetermined distance towards the pivot 32 of the lever 26, that is, to the left in Figures 1, 2 and 5.

It will be appreciated, however, that if the tank E is completely emptied before the tank F is filled, it is desirableto close the valve 23 slightly, and to that end the circuit passes from the transformer Trl, through contacts 46, 41 of the relay Rfl, and contacts 48, 49 of the relay ReZ, since these contacts are closed as soon as the tank E is completely emptied; the circuit then passes on through conductor 59 to the segment is of the distributor switch DS and through the arm 8 also fixed to the shaft 39, and through the motor reversing switch MRS, by way of the conductor 59 in this case instead of the conductor 5| as before. The switch MRS, therefore, gives the motor 34 an impulse in the opposite direction, causing the counterweight 21 to move the same amount further from the pivot 32 of the lever 26,and thereby closing the valve 23 by the predetermined small amount. If the tank F should be filled and the tank E completely emptied at precisely the same instant, it is clear that the relay Ry! is energised at the same moment that the relay Re2 is de-energised, and neither of the above circuits will be completed so that the motor 34 will not receive any impulse and the adjustment of the sludge valve 23 will not be altered.

As an additional safeguard, in the example shown in the drawing, a solenoid 52 (Figures 1, 2, 5 and 6) is mounted on the second valve 23 for the purpose of closing that valve, if in the tank which is being-emptied at any time, such as the tank E, the sludge reaches the low level when the sludge in the vessel F being filled at that time has not reached its high level. This deals with faults likely to cause slow filling, for example, choking in the sludge feed pump, or It also prevents thevessel being emptied from being drained completely, which would be objectionable since it Would allow steam to blow through the heat exchanger employed, thus spoiling its economy.

In the example illustrated, the winding of the solenoid 52 is connected across the conductors 44 and 59 so that if the circuit last described,

above from the transformer Trl were closed on the tankE becoming completely emptied before the tank F were filled, a circuit is also completed branching through conductors 53, energising the winding of solenoid 52. The latter draws up its core 54 which is connected by a link 55 to a second arm 56 of the lever'30. The lever 30 is, therefore, rocked in a clockwise direction, as seen in Figure 5, and the valve member 3l' entirely closed.

In order that the plant may operate when the automatic discharge valves3 and 23 are out of action either through defects or because they 1 are shut offr'by the stop valves'2, 2a, a by-pass pipe 51 is shown in Figure 1 controlled by a stop valve 58, 58a, at either end in such a way that it may by-pass the whole of the automatic control apparatus described above when the stop valves 58, 58a are opened.

It is clear that the details of construction according to the invention are capable of considerable variation. For example, the valves 3 and 23 need not be of the sliding gate type since any type of valve which admits of slight closing or opening will serve. Furthermore, the constant forces provided to balance the pressures in the cylinders 9 and 24 could be provided by springs instead of the counterweights II and 21.

Iv claim:

1. In an installation for the treatment of a iiuid material in a plurality of treatment vessels which are filled with the material and emptied in sequence, the combination of a discharge manifold connected to receive the eflluent from said vessels in sequence, a valve located in said discharge manifold to control the flow f the fluid, second valve also located in said discharge manifold to control the flow of the fluid from said first-named valve, a cylinder, a piston mounted to, slide in said cylinder, a pressure line connecting the space in said discharge manifold between said two. valves to the space in said cylinder to permit the pressure in said space in said discharge manifold to be operative on said piston, a counterweight operative to load said piston in opposition to said pressure, means connecting said piston to said first-named valve to cause the latter'to be-opened upon reduction in the pressure in the space in said discharge manifold. between said two valves, a second cylinder, a piston mounted. to slide in said second cylinder, a second pressure line connecting the space in said discharge manifold between said two valves to the space in saidysecond cylinder to permit the pressure in said space in said discharge manifold to be operative upon said piston in said second cylinder, a second counterweight operative to load said'piston in said second cylinder in opposition to said pressure, means connecting said piston in said second cylinder to said second valve to cause the latter to be moved towards its closing position upon reduction in the pressure in the space in said discharge manifold between said two valves, and means for varying the loading of said piston in said second cylinder due to said second counterweight independence upon the relative times of the filling and emptying of two of said treatmentvessels which are re" spectively filled and emptied at the same time.

2. In an installation for the treatment of a fluid material in a plurality of treatment vessels which are filled with the material and emptied in sequence, the combination of'a discharge manifold connected to receive the effluent from said vessels in sequence, a valve located in said discharge manifold to control the flow of the fluid, a second valvealso located in said discharge manifold to control the-flow of the fluid from said first-named valve, a cylinder, a piston mounted to slide'in said cylinder, a pressure line connecting the space-in said discharge-manifold be-- tween said two valves to the space:in said cylinder to permit the pressure in said space in said discharge manifold to be operative on said piston, a counterweight operative to load said' piston in opposition to said pressure, means connecting said piston to said first-named valve to cause the latter to be opened upon reduction in the pres- Lil) sure in the space in said discharge manifold be-' tween said two valves, a second cylinder, a piston mounted to slide in said second cylinder, a second pressure line connecting the space in said discharge manifold between said two valves to the space in said second cylinder to permit the pressure in said space in said discharge manifold "to be operative upon said piston in said second cylinder, a pivoted lever linked to said piston in said second cylinder, a second counterweight mounted on said pivoted lever for movement towards and from the pivot thereof and operative through said pivoted lever to load said piston in said second cylinder in opposition to said pressure, means connecting said piston in said second cylinder to said second valve to cause the latter to be moved towards its closing position upon reduction in the pressure in the space in said discharge manifold between said two valves, and means for moving said second counterweight towards and from the pivot of said lever to vary the loading of said piston in said second cylinder in dependence upon the relative times of the filling and emptying of two of said treatment vessels which are respectively filled and emptied at the same time.

3. In an installation for the treatment of a fluid material in a plurality of treatment vessels which are filled with the material and emptied in sequence, the combination of a discharge manifold connected to receive the effluent from said vessel in sequence, a valve located in said discharge manifold to control the flow of the fluid, a second valve also located in said discharge manifold to control the flow of the fluid from said first-named valve, a cylinder, a piston mounted to slide in said cylinder, a pressure line connecting the space in said discharge manifold between said two valves to the space in said cylinder to permit the pressure in said space in said discharge manifold to be operative on said piston, a counterweight operative to load said piston in opposition to said pressure, means conmeeting, said piston to said first-named valve to cause the'latter to be opened upon reduction in the pressure in the space in said discharge mani fold between said two valves, a second cylinder, a piston mounted to slide in said second cylinder, a second pressure line connecting the space in said discharge manifold between said two valves to the space in said second cylinder to permit the pressure in said space in said discharge manifold to be operative upon said piston in said second cylinder, a pivoted lever linked to said piston in said second cylinder, a second counterweight mounted on said pivoted lever for movement towards and from the pivot thereof and operative through said pivoted lever to load said piston in said second cylinder in opposition to said pressure, means connecting said piston in said second cylinder to said second valve to cause the latter to be moved towards its closing position upon reductionin the pressure in the space in said discharge manifold between said two valves, a reversible electric motor, gearing connecting said motor to said second counterweight for moving the latter towards or from the pivot of said lever in dependence upon the direction of rotation of 9 I which are respectively filled and emptied at the same time, in the event that the filling and emptying of said two vessels are not completed simultaneously.

4. In an installation for the treatment of a fluid material in a plurality of treatment vessels which are filled with the material and emptied in sequence, the combination of a discharge manifold connected to receive the eflluent from said vessels in sequence, a valv located in said discharge manifold to control the flow of the fluid,

a second valve also located in said discharge manifold to control the flow of the fluid from said first-named valve, a cylinder, a piston mounted to slide in said cylinder, a pressure line connecting the space in said discharge manifold between said two valves to the space in said cylinder to permit the pressure in said space in said discharge manifold to be operative on said piston, a counterweight operative to load said piston in opposition to said pressure, means connecting said piston to said first-named valve to cause the latter to be opened upon reduction in the pressure in the space in said discharge manifold between said two valves, a second cylinder, a piston mounted to slide in said second cylinder, a second pressure line connecting the space in said discharge manifold between said two valves to the space in said second cylinder to permit the pressure in said space in said discharge manifold to be operative upon said piston in said second cylinder, a pivoted lever linked to said piston in said second cylinder, a second counterweight mounted on said pivoted lever for movement towards and from the pivot thereofand operative through said pivoted lever to load said piston in said second cylinder in opposition to said pressure, means connecting said piston in said second cylinder to said second valve to cause the latter to be moved towards its closing position 1 upon reduction in the pressure in the space in said discharge manifold between said two valves, a reversible electric motor, a lead-screw in threaded engagement with said second counterweight and in driving connection with said motor, circuit connections to said motor, and control means in said circuit connections operable in accordance with the levels of materials in said treatment vessels to energise said motor for rotation in one direction or the other in dependence upon the relative times of the filling and emptying of two of said treatment vessels which are respectively filled and emptied at the same time, in the event that the filling and emptying of said two vessels are not completed simultaneously.

5. In an installation for the treatment of a fluid material in a plurality of treatment vessels which are filled with the material and emptied in sequence, the combination of a discharge manifold connected to receive the effluent from said vessels in sequence, a valve located in said discharge manifold to control the flow of the fluid, a second valve also located in said discharge manifold to control the flow of the fluid from said firstnamed valve. a cylinder, a piston mounted to slide in said cylinder, a pressure line connecting the space in said discharge manifold between said two valves to, the space in said cylinder to permit the pressure in said space in said discharge manifold to be operative on said piston, a counterweight operative to load said piston in opposition to said pressure, means connecting said piston to said first-named valve to cause the latter to be opened upon reduction in the pressure in the space in said discharge manifold between said 10 two valves, a second cylinder, a piston mounted to slide in said second cylinder, a second pressure line connecting the space in said discharge manifold between said two valves to the space in said second cylinder to permit the pressure in said space in said discharge manifold to be operative upon said piston in said second cylinder, a pivoted lever linked to said piston in said second cylinder, a second counterweight mounted on said pivoted lever for movement towards and from the pivot thereof and operative through said pivoted lever to load said piston in said second cylinder in opposition to said pressure, means connecting said piston in said second cylinder to said second valve to cause the latter to be moved towards its closing position upon reduction in the pressure in the space in said discharge manifold between said two valves, a reversible electric motor, gearing connecting said motor to said second countei weight for moving the latter towards or from the pivot of said lever in dependence upon the direction of rotation of said motor, circuit connections to said motor and control means in said circuit connections, including a plurality of relays each associated with one of said treatment vessels and operable on the respective vessels being filled and a plurality of relays each associated with one of said treatment vessels and operable on the respective vessels being emptied to energize said motor for rotation in one direction or the other in dependence upon the relative times of the filling and emptying of two of said treatment vessels which are respectively filled and emptied at the same time, in the event that the filling and emptying of said two vessels are not completed simultaneously.

6. In an installation for the treatment of a fluid material in a plurality of treatment vessels which are filled with the material and emptied in sequence, the combination of a discharge manifold connected to receive the effluent from said vessels in sequence, a valve located in said discharge manifold to control the flow of the fluid, a second valve also located in said discharge manifold to control the flow of the fluid from said firstnamed valve, a cylinder, 3, piston. mounted to slide in said cylinder, a pressure line connecting the space in said discharge manifold between said two valves to the space in said cylinder to permit the pressure in said space in said discharge manifold to be operative on said piston, a counterweight operative to load said piston in opposition to said pressure, means connecting-said piston,

to said first-named valve to cause the latter to be opened upon reduction in the pressure in the space in said discharge manifold between said two valves, a second cylinder, a piston mounted to slide in said second cylinder, a second pressure line connecting the space in said discharge mani fold between said two valves to the space in said second cylinder to permit the pressure in said space in said discharge manifold to be operative upon said piston in said second cylinder, a second counterweight operative to load said piston in said second cylinder in opposition to said pressure, means connecting said piston in said second cylinder to said second valve to cause the latter to be moved towards its closing position upon reduction in the pressure in the space in said discharge manifold between said two valves, means for varying the loading of said piston in said second cylinder due to said second counterweight in dependence upon the relative times of the filling and emptying of two of said treatment vessels which are respectively filled and emptied at the same time, a solenoid having its armature operatively connected to said second valve, circuit connected to receive the efiluent from said vessels in sequence, a valve located in said discharge manifold to control the flow of the fluid, a second valve also located in said discharge manifold to control the flow of the fluid from said firstnamed valve, means for biasing said first-named valve towards open position, means responsive to the pressure in said manifold between said valves and tending to move said first named valve towards closed position, means for biasing said second valve towards closed position, and means responsive to the pressure in said manifold benectionsto said :solenoid and control means in said circuit connections operable in the event that one ofsaid treatment vessels which is being emptied is completely emptied before another of said treatment vessels which is being filled at the same time, is .filled to a predetermined level to operate said solenoid-to close said second valve.

WILLIAM KING PORTEOUS.

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